1. Field of the Invention
The present invention relates to a reverse-shift-activated mirror angle control method and apparatus which allow a driver to visually check areas around rear wheels during backing-up (e.g., when backing into a parking space) by turning mirror surfaces of vehicle outer mirrors downward by predetermined amounts simultaneously as gear-shifting means of a vehicle is set to a reverse position and restore the original mirror angles by moving, the mirrors upward by predetermined amounts simultaneously as the gear-shifting means is subsequently switched to another operating position from the reverse position, reducing deviations in a return position caused by repetition of turning operation. Also, it relates to a method and apparatus for detecting a rotation amount of the DC brush motor by counting pulses generated by switching of brushes when a DC brush motor rotates to improve detection accuracy of the rotation amount of the motor during steady-state operation.
However, present claims of this application define the invention of “DC BRUSH MOTOR ROTATION AMOUNT DETECTION METHOD AND APPARATUS”. The invention of “REVERSE-SHIFT-ACTIVATED MIRROR ANGLE CONTROL METHOD AND APPARATUS FOR VEHICLE OUTER MIRROR” corresponds to an invention which utilizes the invention of “DC BRUSH MOTOR ROTATION AMOUNT DETECTION METHOD AND APPARATUS”. The applicants have not abandoned the right to obtain (a) patent(s) about the invention of “REVERSE-SHIFT-ACTIVATED MIRROR ANGLE CONTROL METHOD AND APPARATUS FOR VEHICLE OUTER MIRROR”.
2. Description of the Related Art
Regarding vehicle outer mirrors equipped with a motor-operated mirror angle adjustment mechanism, it has been proposed to add a reverse-shift-activated mirror angle control function (such as the one described above) to them using the motor-operated mirror angle adjustment mechanism and such a function has been put into actual use. To implement the reverse-shift-activated mirror angle control function, it is necessary to detect the turning amount of a mirror surface in order to stop the mirror surface at a predetermined mirror angular position during downward motion and return the mirror surface to the original mirror angular position during upward (return) motion. Thus, as a method for detecting the turning amount of a mirror surface in a simple manner, a method which detects the turning amount of the mirror surface by counting pulses generated by switching of brushes when a DC brush motor, i.e., a power source of the motor-operated mirror angle adjustment mechanism, rotates has been proposed and put into actual use. With this method, however, depending on the type of motor, the temperature around the motor, secular changes, etc., there can be a situation in which noise pulses are detected other than at switching positions of the brushes or pulses are not detected (missing pulses) at switching positions, causing deviations between actual turning amount and pulse count. Consequently, the return position can deviate gradually as downward and return motions are repeated, making it necessary to manually correct the mirror angular position from time to time.
To solve the above problems, techniques described in patent documents 1 and 2 have been proposed. The technique described in patent document 1 involves removing noise pulses using a hardware-based high pass filter and low pass filter. The technique described in patent document 2 involves calculating the average of pulse signal intervals, and then ignoring (not counting) the current pulse by determining it to be a noise pulse if the signal interval between the current pulse and previous pulse is not more than 75% of the average, or counting an extra pulse by determining it to be a missing pulse if the signal interval between the current pulse and previous pulse is not less than 150% of the average.
[Patent document 1] Japanese Patent Laid-Open No. 2004-182126
[Patent document 2] Japanese Patent No. 3547523
The technique described in patent document 1 cannot discriminate a noise pulse from a normal pulse generated by switching of brushes if the pulses are close in frequency band, and thus cannot remove the noise pulse. Also, since the high pass filter and low pass filter are hardware-based, the addition of the hardware will increase costs. With the technique described in patent document 2, since any missing signal can affect (increase) the calculated average, normal pulses generated by switching of the brushes are sometimes removed by being determined to be noise pulses (resulting in missing pulses).